A logic family is a group of devices built around a particular circuit technology and compatible electrical conventions. TTL traditionally uses bipolar transistors; CMOS uses complementary MOS transistors. Compatibility depends on guaranteed input and output levels, supply voltage and drive capability, not just the gate names.
Worked example
Suppose a driver's guaranteed high output is 2.4 V but a receiver requires at least 3.5 V for high. Their high-level specifications do not overlap adequately, so a direct connection is not guaranteed to work. A compatible receiver or level translator is needed.
What to watch for
Avoid assuming every TTL device uses the same limits or every CMOS input accepts another device's voltage. Check both data sheets, including absolute maximum ratings.
Try it yourself
Is matching the AND-gate function enough to prove two devices are electrically compatible?
Answer: No. Their supply, voltage thresholds, output drive and input limits must also support the proposed connection.
How to study this topic
Use the numerical values here as teaching examples. For a physical design, consult the actual component data sheet at the intended supply, load and temperature. Logical equivalence alone does not establish electrical compatibility.
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